JP2013230935A - Image forming device, image forming system, external device and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that can prevent charged sheets from sticking to each other.SOLUTION: An image forming device has a single-sided printing mode in which an image can be printed on the front of a sheet by conveyance in a non-inversion conveyance part, and a duplex printing mode in which an image can be printed on the front and back of a sheet by conveyance in the non-inversion conveyance part and inversion conveyance in an inversion conveyance part. At least the duplex printing mode has an alternate sheet discharge mode that performs alternately: a non-inversion sheet discharge operation in which the sheet is discharged without turning over the sheet by the second sheet inversion part after the image is printed on the frond and back of the sheet by an image forming part; and an inversion sheet discharge operation in which sheet turned over in the second sheet inversion part is discharged. In the alternate sheet discharge mode, the front and back images to be printed on the sheet are preferably printed in reverse order between the non-inversion sheet discharge and the inversion sheet discharge.

Description

 The present invention relates to an image forming apparatus that performs printing on a sheet based on image data, and more particularly to an image forming apparatus, an image forming system, an external apparatus, and an image forming method having a single-sided printing mode and a double-sided printing mode. It is.

In an electrophotographic image forming apparatus, a latent image is formed on a photoconductor based on image data, and the latent image is developed with a toner image. The developed toner image is transferred to a sheet through a transfer unit. In the case where the toner image is once transferred to the intermediate transfer portion, the toner image of the intermediate transfer portion is transferred to the sheet through a transfer portion corresponding to the second transfer portion.
In these transfer portions, in order to perform transfer reliably, a positively charged toner image is attracted to the paper side by applying a positive charge to the back side of the paper to perform the transfer. Thereafter, the toner image is fixed on the paper by the fixing device, and the paper on which the toner image is fixed is discharged to a paper discharge tray.

  Such an image forming apparatus has two modes: a paper discharge mode for discharging the paper with the toner image fixed on the front and back sides of the paper as it is, and a paper discharge mode for discharging the paper with the front and back sides reversed. (For example, refer to Patent Document 1). In such an image forming apparatus, the paper discharge mode can be switched for each job in order to facilitate classification in units of jobs.

JP 2007-168116 A Japanese Patent Laid-Open No. 10-181969 JP 2004-10240 A

  Incidentally, in the image forming apparatus, in the process of transferring the toner image to the paper, a positive charge is applied from the back side of the paper in order to attract the negatively charged toner image to the paper. Due to this influence, the sheet on which the toner image has been transferred is negatively charged on the surface on which the toner image is placed, and the surface on which the opposite positive charge is applied is positively charged.

  When discharging such charged paper to the paper output tray, if the paper is turned with the front and back facing the same as the previously discharged paper, the positive and negative charging surfaces of the paper overlap and the paper There are problems such as sticking together and making it difficult to align the paper. The problem becomes more apparent when post-processing paper. Such a problem occurs particularly remarkably in a printed matter in the field of PP (production printing) machines.

  In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-228561, for each job, two modes are switched between a mode in which the paper is discharged with the front and back sides of the paper as they are and a mode in which the paper is turned upside down and discharged. However, this image forming apparatus cannot prevent sheets discharged in the same job from sticking to each other.

  In view of the above problems, there has been proposed one that discharges paper after image transfer with a discharging blower (see Patent Document 2). In addition, there has been proposed a device in which the first static eliminator and the second static eliminator are provided to ensure static elimination (see Patent Document 3). However, it is difficult to reliably perform such static elimination, and it is impossible to surely prevent sticking between sheets.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide an image forming apparatus capable of preventing charged sheets from sticking to each other.

Of the image forming apparatuses of the present invention, the first aspect of the present invention is an image forming unit that prints an image on a sheet based on image data;
The non-reversing conveyance unit that conveys the sheet to the downstream side in the paper discharge direction without reversing the front and back through the image forming unit and the sheet conveying direction of the image forming unit by reversing the front and back of the sheet printed on one side A transport unit having a reverse transport unit for transporting upstream;
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the front and back of the sheet conveyed by the reversing conveyance unit;
A second paper reversing unit that is provided in the transport unit from the image forming unit to the downstream side in the paper discharge direction and reverses the front and back of the paper transported by the transport unit;
A control unit that controls the image forming unit and the transport unit;
The control unit includes the one-sided printing mode in which an image can be printed on the front side of the sheet by conveyance in the non-reversing conveyance unit, conveyance in the non-reversing conveyance unit, and reversal conveyance in the reverse conveyance unit. A double-sided printing mode in which images can be printed on the front and back of the paper, and at least in the double-sided printing mode, after the image is printed on the front and back of the paper by the image forming unit, the front and back of the paper are reversed by the second paper reversing unit. A non-reverse paper discharge operation for discharging paper without being reversed and a reverse paper discharge operation for performing paper discharge by reversing the front and back of the paper at the second paper reversing unit are alternately performed for each paper to be discharged. It has a paper discharge operation mode.

  According to the present invention, the non-reverse paper discharge operation for discharging the paper without reversing the front and back of the paper by the second paper reversing unit after the image is printed on the paper, and the paper at the second paper reversing unit after the image printing is performed. The reverse paper discharge operation, which reverses the front and back of the paper, is performed alternately for each paper to be discharged, so the positively charged surface and the negatively charged surface of the paper do not overlap, making it easier for the paper to stick together Can be prevented.

  An image forming apparatus according to a second aspect of the present invention is characterized in that, in the first aspect of the present invention, the non-reversing conveyance unit includes a straight conveyance unit that discharges a sheet straight.

  According to the present invention, the non-reversing paper discharge operation can be performed through the straight conveyance unit.

  In the image forming apparatus according to a third aspect of the present invention, in the first or second aspect of the present invention, the non-inverted conveyance unit has a detour conveyance unit, and the detour conveyance unit does not pass through the detour conveyance unit. It has a longer path length than a path for discharging the paper straight.

  In the image forming apparatus according to the fourth aspect of the present invention, in the second or third aspect of the present invention, the path length of the detour conveyance unit and the path length via the second sheet reversing unit are continuously conveyed. The path of the detour conveyance unit and the path via the sheet reversing unit have a relationship that does not interfere with each other on the downstream conveyance unit between the sheets.

  In the image forming apparatus of the fifth aspect of the present invention, in any one of the second to fourth aspects of the present invention, the path length of the detour conveyance unit and the path length through the second sheet reversing unit are substantially the same. It is characterized by being.

  The image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to any one of the second to fifth aspects, wherein the sheet is conveyed through the detour conveyance unit and the second sheet reversing unit. The transport time to be conveyed does not interfere with each other on the downstream transport unit where the path of the detour transport unit and the path via the paper reversing unit merge between continuously transported sheets. Features.

  An image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to any one of the second to sixth aspects of the present invention, wherein the sheet is conveyed through the detour conveyance unit and conveyed through the second sheet reversing unit. The transporting time is substantially the same.

When the non-reverse paper discharge operation and the reverse paper discharge operation are alternated, the path length is usually longer in the conveyance through the second paper reversing unit than in the straight conveyance. The conveyance time is longer when the sheet is conveyed through the sheet reversing unit 2 than when the sheet is conveyed straight. For this reason, if the sheet is straightly conveyed by the non-reverse sheet discharge operation as it is, there is a possibility that the sheet is reversed by the second sheet reversing unit according to the reverse sheet discharge operation and interferes with the sheet immediately before being conveyed downstream. In order to avoid this, it is conceivable to reduce the conveying speed in straight paper discharge or lengthen the gap between the sheets, but this causes a decrease in productivity. In order to maintain productivity, it is conceivable to increase the conveyance speed of the path via the second sheet reversing unit, but the conveyance stability is impaired by increasing the conveyance speed.
According to the third to seventh aspects of the present invention, the sheet can be conveyed through a path longer than the straight conveyance by performing the conveyance through the detour conveyance unit during the non-reversing paper discharge operation. As a result, while avoiding a decrease in productivity or reducing a decrease in productivity, it is possible to suppress a decrease in the gap between the sheet that performs the reverse discharge operation and the paper that performs the non-reverse discharge operation. Interference between each other can be prevented. In addition, when a straight conveyance unit is provided, it is possible to perform paper conveyance by selecting either the detour conveyance unit or the straight conveyance unit when performing non-reversal paper discharge operation, such as when there is no need to consider a decrease in productivity. .
If the path lengths of the detour conveyance unit and the second reverse conveyance unit are the same, or if the conveyance times of the detour conveyance unit and the second reverse conveyance unit are the same, the paper in the non-reverse operation and the reverse operation It is possible to keep the gap between the papers constant.

  An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to any one of the first to seventh aspects of the present invention, wherein the control unit applies the non-reverse discharge operation to the sheet on which the non-reverse discharge operation is performed in the alternate discharge operation mode. In the image formation and the image formation on the paper on which the reverse paper discharge operation is performed, printing is performed by reversing the page order of the front image and the back image printed on the paper for each sheet.

  According to the present invention, in the image formation in which the non-reverse paper discharge operation or the reverse paper discharge operation is performed, the front image and the back image to be printed on the paper are reversed and printed in reverse to the other operation. The images can be ejected while keeping the order of the images to be properly maintained in the page order.

  An image forming apparatus according to a ninth aspect of the present invention is characterized in that, in any one of the first to eighth aspects of the present invention, the control unit performs the alternate paper discharge operation mode only in the duplex printing mode.

  The image forming apparatus according to a tenth aspect of the present invention is the image forming apparatus according to any one of the first to ninth aspects of the invention, wherein the control unit performs the alternate discharge when the image forming unit prints using clear toner. It operates in an operation mode.

  According to the present invention, since printing is performed in the alternate paper discharge operation mode in the case of printing using clear toner, it is possible to prevent the sheets from sticking to each other.

  An image forming apparatus according to an eleventh aspect of the present invention is the image forming apparatus according to any one of the first to tenth aspects, wherein the control unit is configured to perform the alternate discharge operation mode when the toner adhesion amount or the printing rate is equal to or greater than a predetermined value. It is characterized by operating in.

According to the present invention, since the charge amount of the paper tends to be large, the printing operation is performed in the alternate paper discharge operation mode when the toner adhesion amount is a predetermined value or more and the printing rate is the predetermined value or more, so the papers stick to each other. Can be prevented.
As the printing rate, there are a clear toner printing rate and a colored toner printing rate.

  An image forming apparatus according to a twelfth aspect of the present invention is the image forming apparatus according to any one of the first to eleventh aspects, wherein the control unit operates in the alternate paper discharge operation mode when a post-processing apparatus is connected. It is characterized by that.

  According to the present invention, since the sheets are operated in the alternate sheet discharge operation mode when the post-processing apparatus is connected, it is possible to prevent the sheets from easily sticking to each other.

  The image forming apparatus according to a thirteenth aspect of the present invention is the image forming apparatus according to any one of the first to twelfth aspects, wherein the control unit determines whether to operate in the alternate paper discharge operation mode based on the type of the paper. It is characterized by doing.

  According to the present invention, since the sheet is operated in the alternate sheet discharge operation mode when the sheet type is easily charged, it is possible to prevent the sheets from sticking to each other. The type of paper that is easily charged is, for example, coated paper.

  An image forming apparatus according to a fourteenth aspect of the present invention is the image forming apparatus according to any one of the first to thirteenth aspects, wherein the control unit is configured to perform printing of the image when the single-sided printing mode is set. The method is characterized in that a blank image is set as an image to be printed on the opposite paper surface, duplex printing is performed, and the operation is performed in the alternate paper discharge operation mode.

  According to the present invention, when the single-sided printing mode is set, the blank image is set as the image to be printed on the side opposite to the side on which image printing is performed, and duplex printing is performed. Since it operates, it is possible to prevent the sheets from sticking to each other even in single-sided printing sheets.

  An image forming apparatus according to a fifteenth aspect of the present invention is the image forming apparatus according to any one of the first to fourteenth aspects, wherein when the control unit starts a job in the alternate paper discharge operation mode, When the non-reverse paper discharge is performed, the job is started by the reverse paper discharge, and when the reverse paper discharge is performed at the end of the immediately preceding job, the job is started by the non-reverse paper discharge. .

  According to the present invention, when starting a job, if the non-reverse discharge is performed at the end of the previous job, the reverse discharge is started, and the reverse discharge is performed at the end of the previous job. If it is performed, the job is started with the non-inverted sheet discharge, so that the sheets can be prevented from sticking to each other.

  An image forming apparatus according to a sixteenth aspect of the present invention is the image forming apparatus according to any one of the first to fifteenth aspects, wherein the control unit interrupts when resuming printing interrupted during the operation in the alternate paper discharge operation mode. When the last normal discharge operation is the non-reverse discharge operation, the job is resumed with the reverse discharge, and the last normal discharge operation before the interruption is the reverse discharge operation. In this case, the job is resumed by the non-inverted discharge.

  According to the present invention, when the interrupted printing is resumed, if the operation that normally ejects paper at the end before the interruption is the non-reversed paper ejection, the job is resumed with the reverse paper ejection, When the last normal paper discharge operation is the reverse paper discharge, the job is resumed by the non-reverse paper discharge, so that the sheets can be prevented from sticking to each other.

An image forming system according to a seventeenth aspect of the present invention is
An image forming unit that prints an image on paper based on image data;
The sheet printed on one side is reversed with a non-reversing conveying section that conveys the sheet to the downstream side in the paper discharge direction via the image forming section and a non-reversing conveying section that conveys the sheet via the image forming section. A transport unit having a reverse transport unit that transports the image forming unit to the upstream side in the paper transport direction;
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the sheet conveyed by the reversing conveyance unit;
A second paper reversing unit that is provided in the transport unit from the image forming unit to the downstream side in the paper discharge direction and reverses the paper transported by the transport unit;
A control unit that controls the image forming unit and the transport unit;
The control unit includes the one-sided printing mode in which an image can be printed on the front side of the sheet by conveyance in the non-reversing conveyance unit, conveyance in the non-reversing conveyance unit, and reversal conveyance in the reverse conveyance unit. A double-sided printing mode in which images can be printed on the front and back of the paper, and at least in the double-sided printing mode, after the image is printed on the front and back of the paper by the image forming unit, the front and back of the paper are reversed by the second paper reversing unit. A non-reverse discharge operation that discharges paper without being discharged and a reverse conveyance operation that reverses the front and back of the paper and discharges the paper at the second paper reversing section are alternately switched for each paper to be discharged. It has a paper operation mode.

An image forming system according to an eighteenth aspect of the present invention is the seventeenth aspect of the present invention,
The non-reversing transport unit includes a straight transport unit that discharges the paper straightly downstream in the paper discharge direction.

According to a nineteenth aspect of the present invention, in the seventeenth or eighteenth aspect of the present invention,
The non-reversing conveyance unit includes a detour conveyance unit, and the detour conveyance unit has a longer path length than a path for discharging the paper straight without passing through the detour conveyance unit.

The external device of the twentieth aspect of the present invention is
An image forming unit that prints an image on paper based on image data;
A transport unit having a non-reverse transport unit that transports the paper through the image forming unit and a reverse transport unit that reverses the paper printed on one side and transports the paper upstream of the image forming unit in the paper transport direction; ,
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the sheet conveyed by the reversing conveyance unit;
A control unit according to any one of the first to nineteenth aspects of the present invention, connected to the downstream side in the paper discharge direction of an image forming apparatus,
A second sheet reversing unit according to any one of the first to nineteenth aspects of the present invention is provided.

The image forming method of the twenty-first aspect of the present invention is
In an image forming method for printing an image on the front and back of a sheet based on image data,
An image is printed on the front and back of the paper by non-reversing transport that transports the paper without reversing and reversal transport that transports the paper by reversing the front and back of the paper, and then ejects the paper without reversing the front and back of the paper. A non-reverse paper discharge operation for discharging the paper downstream in the paper direction and a reverse paper discharge operation for reversing the front and back of the paper and discharging the paper downstream in the paper discharge direction are alternately switched for each paper to be discharged. It is characterized by that.

  An image forming method according to a twenty-second aspect of the present invention is the image forming method according to the twenty-first aspect, wherein the image is formed on the sheet on which the non-reverse conveyance is performed and the image is formed on the sheet on which the reverse conveyance is performed. It is characterized in that printing is performed with the page order of the front and back images reversed every other page.

  As described above, according to the present invention, after image printing on paper, the paper reversing unit discharges paper without reversing the front and back, and after image printing, the paper reversing unit turns the paper back and front. Reverse paper discharge that reverses and discharges paper is switched alternately for each paper to be discharged, so that the positively charged surface and negatively charged surface of the paper do not overlap, preventing the paper from sticking together Can do.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. Similarly, it is a control block diagram. Similarly, it is a figure which shows the operation | movement at the time of straight discharge. Similarly, it is a figure which shows the operation | movement at the time of reverse discharge. Similarly, it is a figure which shows the paper conveyance operation | movement at the time of duplex printing. Similarly, it is a flowchart showing a printing procedure. Similarly, it is a flowchart illustrating a procedure for determining whether or not to alternately discharge paper. Similarly, it is a flowchart showing a procedure for determining whether or not alternate discharge is necessary in another example. Similarly, it is a flowchart showing a procedure for determining whether or not alternate discharge is necessary in another example. Similarly, it is a flowchart showing a procedure for determining the image page order and paper discharge mode. It is a figure which shows the structure of the image forming apparatus of other embodiment of this invention. Similarly, it is a control block diagram. Similarly, it is a figure which shows the operation | movement at the time of detour discharge. Similarly, it is a figure which shows the operation | movement at the time of reverse discharge. Similarly, it is a figure which shows the paper conveyance operation | movement at the time of duplex printing. Similarly, it is a flowchart showing a printing procedure. Similarly, it is a flowchart showing a procedure for determining whether or not alternate discharge is necessary in another example. 1 is a diagram illustrating a configuration of an image forming system according to an embodiment of the present invention. Similarly, it is a control block diagram. Similarly, it is a figure which shows the operation | movement at the time of detour discharge. Similarly, it is a figure which shows the operation | movement at the time of reverse discharge. Similarly, it is a flowchart showing a printing procedure. It is a figure which shows the structure of the image forming apparatus of other embodiment of this invention. It is a figure which shows the principal part structure of further another embodiment of this invention.

An image forming apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows the configuration of the image forming apparatus 1. The image forming apparatus 1 includes a printer 10, an operation panel 80, and a document reading unit 90. The printer 10 prints an image on a sheet based on image data. The operation panel 80 receives operations from the user such as start of printing and selection of a printing mode (double-sided printing mode, high gloss mode, etc.). The document reading unit 90 reads the document and generates image data.

  A transfer belt 12 is disposed at the center of the printer 10. The transfer belt 12 is rotationally driven in the direction of arrow A, and a toner image formed on the surface of the photosensitive drum is primarily transferred onto the transfer belt 12. Then, the toner image on the transfer belt 12 subjected to the primary transfer is secondarily transferred to the paper S.

  On the side surface of the transfer belt 12, five image forming units 14CL, 14Y, 14M, 14CY, and 14K (in order of clear, yellow (Y), magenta (M), cyan (C), and black (K) from the top. In the following, the reference numerals are simplified and indicated by 14). Each image forming unit 14 has a photosensitive drum (not shown). Around each photosensitive drum, a charger for uniformly charging the surface of the photosensitive drum, an exposure unit for forming an electrostatic latent image according to image data on the surface of the uniformly charged photosensitive drum, and the electrostatic latent image as a toner A developing device for developing the image is arranged (none of them are shown).

  In addition, primary transfer rollers 15CL, 15Y, 15M, 15CY, and 15K (hereinafter, the reference numerals are simply indicated by 15) are disposed at positions facing the respective photosensitive drums with the transfer belt 12 interposed therebetween. The primary transfer roller 15 electrostatically attracts the toner image formed on the surface of the photosensitive drum and performs primary transfer onto the transfer belt 12.

  A secondary transfer roller 16 is disposed below the transfer belt 12. The secondary transfer roller 16 secondarily transfers the toner image formed on the transfer belt 12 onto the conveyed paper S. When performing secondary transfer, a negatively charged toner image is electrostatically attracted to the sheet S by applying a high positive transfer voltage to the secondary transfer roller 16.

  A fixing unit 40 for fixing the transferred toner image on the paper S is disposed on the downstream side of the secondary transfer roller 16. Further, on the further downstream side of the fixing unit 40, a paper discharge roller 42 that discharges the paper S to the paper discharge tray 70 via the switching gate 43 is disposed. The paper discharge roller 42 and the paper discharge tray 70 constitute a paper discharge unit.

Two-stage paper feed cassettes 30 and 32 are detachably disposed below the printer 10. A conveyance path 35 is provided from the sheet feeding cassettes 30 and 32 to the sheet discharge tray 70 via the intermediate conveyance roller 34, the registration roller 38, the secondary transfer roller 16, the fixing unit 40, and the sheet discharge roller 42. Each of the rollers and the conveyance path 35 constitute a non-reverse conveyance unit. In this embodiment, the non-reversing conveyance unit is configured as a straight conveyance unit, and the conveyance unit from the image forming unit to the downstream side in the paper discharge direction is configured as a non-reversing conveyance unit.
Further, on the upper side of the sheet feeding cassettes 30 and 32, immediately downstream of the fixing unit 40, is branched from the conveyance path 35 via the switching gate 43 and immediately before the registration roller 38 positioned upstream in the sheet conveyance direction of the image forming unit. A reverse conveyance path 45 that joins the conveyance path 35 is provided.

An ADU reverse roller 46 and an ADU intermediate transport roller 48 that reverse the front and back of the paper S and transport the paper downstream of the reverse transport path 45 are provided on the downstream side of the reverse transport path 45. These rollers and the reverse conveyance path 45 constitute a reverse conveyance unit of the present invention, and a part of the reverse conveyance path 45 located near the upstream and downstream in the conveyance direction of the ADU reverse roller 46 and the ADU reverse roller 46 is the first sheet reverse. Parts.
A reversing conveyance path 45 located immediately below the conveyance path 35 from the fixing unit 40 to the paper discharge roller 42 is a conveyance / conveyance mechanism that reverses the front and back of the paper conveyed from the fixing unit 40 and conveys it to the paper discharge roller 42. A reversing roller 44 is disposed. A part of the conveyance / reverse roller 44 and the reverse conveyance path 45 located in the vicinity of the conveyance direction of the conveyance / reverse roller 44 constitutes a second sheet reversal unit. In this embodiment, the two sheet reversing sections are also used as a part of the reversing conveyance section, but they may have an independent configuration.
In this embodiment, the second sheet reversing unit is provided in the non-reversing conveying unit which is the conveying unit. However, the second reversing conveying unit is provided separately from the non-reversing conveying unit and the second reversing conveying unit is provided. It is also possible to provide a sheet reversing unit. In this case, the second reverse conveyance unit is included in the conveyance unit.

Next, control blocks of the image forming apparatus 1 will be described with reference to FIG.
The printer control unit 100 controls the entire image forming apparatus such as image formation on the paper S, conveyance and discharge of the paper S, and the CPU, a program for operating the CPU, and a storage unit such as ROM and RAM. It is configured. The printer control unit 100 corresponds to the control unit of the present invention.

  A document reading unit 90 is connected to the printer control unit 100 in a controllable manner. The document reading unit 90 reads an image of a document set in the unit and generates image data.

  An operation panel 80 is connected to the printer control unit 100 in a controllable manner. The operation panel 80 accepts operations from the user such as start of printing and selection of a printing mode (double-sided printing mode, high gloss mode, etc.). The operation content is transmitted to the printer control unit 100.

  An image forming unit 110 is connected to the printer control unit 100 in a controllable manner. The image forming unit 110 forms a toner image on the photosensitive drum based on the image data, and primarily transfers the formed toner image onto the transfer belt 12. Then, the toner image on the transfer belt 12 is secondarily transferred onto the sheet S conveyed on the secondary transfer roller 16.

  A fixing unit 40 is connected to the printer control unit 100 in a controllable manner. The fixing unit 40 fixes the toner image transferred onto the paper S to the paper S by heat melting.

  The printer control unit 100 is connected to a paper feed unit 120 in a controllable manner. The sheet feeding unit 120 is a control unit until the sheets S stacked and accommodated in the sheet feeding cassettes 30 and 32 are conveyed to the registration rollers 38 by the intermediate conveying rollers 34.

  The printer control unit 100 is connected to the registration conveyance unit 130 in a controllable manner. The registration conveyance unit 130 is a control unit until the sheet S is conveyed from the registration roller 38 to the fixing unit 40.

  A straight paper discharge unit 140 is connected to the printer control unit 100 in a controllable manner. The straight paper discharge unit 140 is a control unit that discharges the paper S that has passed through the fixing unit 40 to the paper discharge tray 70 by the paper discharge roller 42 without reversing the front and back.

  A reverse paper discharge unit 150 is connected to the printer control unit 100 in a controllable manner. The reverse paper discharge unit 150 is a control unit that discharges the paper S that has passed through the fixing unit 40 to the paper discharge tray 70 by reversing the front and back of the paper by the transport / reverse roller 44.

  An ADU transport unit 160 is connected to the printer control unit 100 in a controllable manner. The ADU transport unit 160 is a control unit until the sheet S that has passed through the fixing unit 40 is reversed by the transport / reverse roller 44 and the ADU reverse roller 46 and transported to the registration roller 38 by the ADU intermediate transport roller 48.

The basic operation of the image forming apparatus 1 will be described below.
When the user performs a print start operation from the operation panel 80, the document reading unit 90 reads the set document and generates image data. Then, based on the generated image data, an electrostatic latent image is formed on the surface of the photosensitive drum uniformly charged by the exposure means. The formed electrostatic latent image is developed into a toner image by a developing device. Then, the toner image formed on the surface of the photosensitive drum is electrostatically attracted by the primary transfer roller 15 to be primarily transferred onto the transfer belt 12. Note that the method of acquiring image data is not limited to the above, and may be acquired via a network.

  Further, according to the print start operation, the paper S stacked and accommodated in the paper feed cassettes 30 and 32 is sent one by one to the transport path 35 by the control of the paper feed unit 120, and the intermediate transport roller 34 transports the transport path 35. Then, the sheet S is conveyed to the registration roller 38. The sheet S conveyed to the registration roller 38 is conveyed to a contact position with the secondary transfer roller 16 in synchronization with the toner image on the transfer belt 12.

  Then, the toner image on the transfer belt 12 is secondarily transferred to the paper S at the position of the secondary transfer roller 16. In the secondary transfer, a high positive transfer voltage is applied to the secondary transfer roller 16 so that a negatively charged toner image is electrostatically attracted from the transfer belt 12 to the sheet S and transferred. The toner image transferred to the paper S is sent through the conveyance path 35 and is fixed to the paper S by heat melting in the fixing unit 40. Thereafter, in the single-sided printing mode, the paper S is discharged to the paper discharge tray 70 through the paper discharge roller 42.

  Note that there are two types of paper discharge modes to the paper discharge tray 70: straight paper discharge and reverse paper discharge. The straight paper discharge is a paper discharge mode in which paper is discharged onto the paper discharge tray 70 without reversing the front and back of the paper S after printing an image on the paper S. In straight paper discharge, paper is discharged face up. The reverse discharge is a discharge mode in which the front and back sides of the paper S are reversed after the image is printed on the paper S and discharged to the paper discharge tray 70. In reverse paper discharge, paper is discharged face down.

  FIG. 3 shows a sheet conveying operation for straight sheet discharge. In the straight sheet discharge, the sheet S that has passed through the fixing unit 40 is transported to the sheet discharge roller 42 without being turned upside down under the control of the straight sheet discharge unit 140, and then passes through the sheet discharge roller 42 to the sheet discharge tray 70. The paper is ejected.

  Next, FIG. 4 shows a reverse paper discharge operation. In reverse paper discharge, the paper S that has passed through the fixing unit 40 is transported to the transport / reverse roller 44 side by the switching operation of the switching gate 43 under the control of the reverse paper discharge unit 150. At this time, the transport / reverse roller 44 is driven to rotate forward, and transports the paper S downward through the reverse transport path 45. Thereafter, the transport / reverse roller 44 is driven in reverse to transport the paper S from the reverse transport path 45 to the discharge roller 42 side. As a result, the sheet S is turned upside down. The sheet S with the front and back sides reversed is discharged to the discharge tray 70 through the discharge roller 42.

Note that the image forming apparatus according to the present embodiment has a double-sided printing mode in which images can be printed on both the front and back sides of a sheet. FIG. 5 shows the operation in the duplex printing mode.
The sheets S stacked and housed in the sheet feeding cassettes 30 and 32 are straightly conveyed to the secondary transfer roller 16 through the conveyance path 35 via the intermediate conveyance roller 34 and the registration roller 38 under the control of the registration conveyance unit 130. . Then, the toner image is transferred to one side of the sheet S by the secondary transfer roller 16 and fixed to the sheet S by the fixing unit 40.

  The sheet S that has passed through the fixing unit 40 is transported to the transport / reverse roller 44 side by switching the switching gate 43, and the ADU reverse roller is driven to rotate forward through the reverse transport path 45 by the transport / reverse roller 44 that is driven to rotate forward. It is conveyed to 46. The sheet S transported to the ADU reverse roller 46 is temporarily stopped at that position, and then the ADU reverse roller 46 is driven in reverse to be transported to the ADU intermediate transport roller 48, and is transported to the registration roller 38 by the ADU intermediate transport roller 48. Is done. At this time, the sheet S is conveyed reversely to the registration roller 38 with the front and back sides reversed.

  Then, the sheet S conveyed to the registration roller 38 is conveyed to the secondary transfer roller 16 through the conveyance path 35, the toner image is transferred to the other surface of the sheet S, and the fixing unit 40 fixes the toner image. Is called. Thereafter, the sheet S is discharged to the discharge tray 70 through the discharge roller 42.

A charging state when the sheet S is image-transferred and discharged will be described. As described above, when the image is transferred to the paper S, the toner is negatively charged, so that the toner is positively transferred from the back side of the paper in the vicinity of the secondary transfer roller 16 so that the toner is reliably transferred to the paper S. To attract the toner to the paper side. As a result, in the sheet S after image transfer, the upper surface side is negatively charged and the lower surface side is positively charged. When this sheet is discharged and accumulated as it is, the front and back surfaces (side1, side2) of the front and rear sheets are in a positive and negative charged state, and a phenomenon occurs in which the sheets are attracted to each other and are attracted to each other.
In the present embodiment, when printing is performed in the duplex printing mode, the straight discharge and the reverse discharge described above are alternately performed, so that side 1 or side 2 of the sheets face each other and repulsive force acts on the sheets. , Prevent mutual adhesion.

Hereinafter, the printing procedure of the image forming apparatus according to the present embodiment will be described with reference to the flowchart of FIG. The following procedure is executed by the printer control unit 100.
When the user performs an operation to start printing from the operation panel 80, it is determined whether or not the received job needs to be operated in an alternate paper discharge operation mode for preventing sticking between sheets (step s1). The alternate paper discharge operation mode is an operation mode in which paper discharge is performed by alternately switching between straight paper discharge and reverse paper discharge for each paper to be discharged. The necessity determination process for the alternate paper discharge operation mode will be described later.

Next, it is determined whether the alternate discharge operation mode is necessary. If alternate discharge is necessary (Yes in step s2), straight discharge and reverse discharge are performed for each sheet included in the job. The alternate paper discharge mode to be switched is set to reverse the image page order for each sheet, and the image page order and paper discharge mode are determined (step s3). The procedure for determining the image page order and paper discharge mode will be described later. On the other hand, if it is not determined that the alternate discharge is necessary (No in step s2), the discharge mode is set to the user designation mode, and the image page order is set to the default setting (step s4). The default setting is usually forward or reverse.
Paper printing processing is performed according to the determined paper discharge mode and image page order (step s5).
In the paper printing process (step s5), the image forming unit 110, the fixing unit 40, and the like are instructed to execute the printing process (image formation, fixing, etc.) for one sheet. At this time, the image formation on the paper is performed in the order of the image pages determined in the process of step s3 or step s4.

Next, it is confirmed whether there is no paper or jam has occurred (step s6). If there is no sheet and no jam has occurred (step s6, No), the process waits until the printing process for one sheet is completed (step s7, No).
If there is no paper or jam occurs during the printing process on the paper (step s6, Yes), the printing process on the paper is interrupted (step s12), and the process waits until the recovery process is completed (step s13, No). ). In the recovery process, replenishment of paper, removal of Jam paper, and the like are performed. When the recovery process is completed (step s13, Yes), the printing process is resumed from the interrupted sheet (to step s5).

When the printing process is completed (step s7, Yes), it is determined whether or not the paper discharge mode of the paper for which the printing process has been completed is reverse paper discharge (step s8). In the alternate paper discharge operation mode, a paper discharge mode different from the previous paper discharge mode is set. That is, if the previous discharge is reverse discharge, it is not reverse discharge (step s8, No), and the straight discharge unit 140 is instructed to execute straight discharge (step s9). If the previous discharge is straight discharge Is the reverse paper discharge (step s8, Yes), and instructs the reverse paper discharge unit 150 to execute the reverse paper discharge (step s10).
If the alternate paper discharge mode is not selected, the straight paper discharge unit 140 is instructed to execute the straight paper discharge (step s9). In the reverse paper discharge (step s8, Yes), the reverse paper discharge unit 150 is instructed to execute the reverse paper discharge (step s10).

  After executing the paper discharge process (step s9 or step s10), the printer control unit 100 checks whether or not the paper on which the paper discharge process has been executed is the final paper of the job being executed (step s11). If it is not the final sheet (step s11, No), a sheet printing process (step s5) on the next sheet is executed. If it is the last sheet (step s11, Yes), the process is terminated.

  As described above, when it is determined that it is necessary to operate in the alternate paper discharge operation mode, the straight paper discharge and the reverse paper discharge are alternately switched for each paper to be discharged. The charged surface and the negatively charged surface do not overlap each other, and sticking between sheets can be prevented.

  Also, in the above process, when there is no paper or jam occurs and printing is interrupted, the printing process is resumed from the interrupted paper. When resuming, the paper is ejected according to the paper ejection mode set for each paper, so the paper ejection mode for the paper ejected immediately before the interruption is different from the paper ejection mode for the paper to be resumed (interruption). Reverse discharge when the paper discharged immediately before is straight discharge, and straight discharge when the paper discharged immediately before interruption is reverse discharge. For this reason, even if printing is interrupted, it is possible to prevent the paper ejected immediately before the interruption and the paper ejected immediately after restarting from being easily stuck.

Next, an example of the procedure of the above-described alternating discharge necessity determination process will be described based on the flowchart of FIG. This processing procedure is executed under the control of the printer control unit 100.
First, it is determined whether or not the duplex printing mode is set (step s20). If the duplex printing mode is not set (step s20, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s23). On the other hand, if the duplex printing mode is set (step s20, Yes), it is determined whether the high gloss mode is set (step s21). If the high gloss mode is not set (step s21, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s23). On the other hand, when the high gloss mode is set (step s21, Yes), it is determined that it is necessary to operate in the alternate paper discharge operation mode (step s22).

  The high gloss mode is a print mode that can be selected by the user. Glossiness is obtained by placing clear toner on the toner images of yellow (Y), magenta (M), cyan (C), and black (K). This mode prints high-quality printed matter. Clear toner has higher resistance than colored toner and tends to hold electric charge. For this reason, a sheet printed in a high gloss mode using clear toner tends to have a large charge amount, and the sheets tend to stick to each other. Therefore, in the high gloss mode and the double-sided printing mode, the operation is performed in the alternate paper discharge operation mode that prevents the sheets from sticking to each other.

  In this example, when it is not the double-sided printing mode, it is determined that it is not necessary to operate in the alternate paper discharge operation mode. However, when single-sided printing is included in a double-sided printing job, you can set a blank image as an image to be printed on the side opposite to the side on which image printing is performed even for single-sided printing. Printing may be performed to operate in the alternate paper discharge operation mode to prevent sticking between sheets.

Next, another example of the alternate discharge necessity determination processing procedure will be described based on the flowchart of FIG. In this example, the processing contents are changed depending on the clear toner printing rate.
The printer control unit 100 determines whether or not the duplex printing mode is set (step s30). If the duplex printing mode is not set (step s30, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s36). On the other hand, when the duplex printing mode is set (step s30, Yes), it is determined whether the clear toner printing rate is 30% or more (step s31). If the clear toner printing rate is 30% or more (step s31, Yes), it is determined that it is necessary to operate in the alternate paper discharge operation mode (step s35). As the clear toner printing rate in the above determination, for example, an average printing rate in a job, an average printing rate for each division in the job, or the like can be used.

On the other hand, if the clear toner printing rate is not 30% or more (step s31, No), it is determined whether a post-processing device is connected to the image forming apparatus (step s32). When the clear toner printing rate is less than 30%, the clear toner is not included.
If the post-processing device is not connected (No at step s32), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s36).
If the post-processing device is connected (step s32, Yes), it is determined whether the paper to be printed is coated paper (step s33). If the paper to be printed is not coated paper (step s33, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s36). If the paper to be printed is coated paper (step s33, Yes), it is determined whether the color toner printing rate is 50% or more (step s34). If the color toner printing rate is not 50% or more (step s34, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s36). On the other hand, when the color toner printing rate is 50% or more (step s34, Yes), it is determined that it is necessary to operate in the alternate paper discharge operation mode (step s35).

Clear toner has higher resistance than colored toner and tends to hold electric charge. For this reason, the charge amount of the paper using the clear toner is likely to increase, and the papers are likely to stick to each other. Therefore, when the clear toner printing rate (attachment amount) is equal to or greater than a predetermined value (30% in this example), the operation is performed in an alternate paper discharge operation mode that prevents sticking between sheets. In addition, the said predetermined value is not specifically limited as this invention, An appropriate setting is possible and you may make it possible to change the set predetermined value.
In this embodiment, it is determined whether the operation of the alternate paper discharge operation mode is necessary depending on the toner printing rate. However, the determination is made based on whether the amount of toner attached to the sheet is a predetermined value or more. Also good. Also in the toner adhesion amount determination, an average adhesion amount in a job or a section can be used. An appropriate value can be set as the predetermined value of the toner adhesion amount.

The post-processing device connected to the image forming apparatus provides finishing functions for printed paper such as side-stitching, saddle-stitching, folding, punching, and the like. Greatly affects. In consideration of post-processing having a great influence, whether or not the alternate paper discharge mode is selected may be set according to the type of post-processing.
Also, the higher the sheet resistance, the greater the amount of charge on the sheet. For example, coated paper has a higher resistance than uncoated paper, and the amount of charge on the paper tends to increase.
Further, since the resin layer contained in the toner easily holds the charge, the charge amount of the paper having a high toner printing rate (attachment amount) tends to be large. Therefore, when the post-processing device is connected, the paper is coated paper, and the color toner printing rate is equal to or higher than a predetermined value (for example, 50%), the clear toner printing rate is less than 30%. However, the operation is performed in an alternate paper discharge operation mode that prevents the sheets from sticking to each other. In this case, a predetermined value may be determined for each color, or a predetermined value may be determined for a specific color toner.

Next, still another example of the alternate paper discharge necessity determination processing procedure will be described based on the flowchart of FIG. In this example, the processing contents are changed depending on whether or not the mode is the high gloss mode and the print rate of the clear toner in the high gloss mode.
It is determined whether the duplex printing mode is set (step s40). If the duplex printing mode is not set (step s40, No), it is determined that there is no need to operate in the alternate paper discharge operation mode (step s47). On the other hand, when the duplex printing mode is set (step s40, Yes), it is determined whether the mode is the high gloss mode (step s41). When the high gloss mode is not set (step s41, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s47). On the other hand, when the high gloss mode is set (step s41, Yes), it is determined whether or not the clear toner printing rate is 30% or more (step s42). If the clear toner printing rate is 30% or more (step s42, Yes), it is determined that it is necessary to operate in the alternate paper discharge operation mode (step s46).

On the other hand, if the clear toner printing rate is less than 30% (No in step s42), it is determined whether the post-processing device is connected to the image forming apparatus (step s43).
If the post-processing apparatus is not connected (No at step s43), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s47). If the post-processing device is connected (step s43, Yes), it is determined whether the paper to be printed is coated paper (step s44). If the paper to be printed is not coated paper (step s44, No), it is determined that there is no need to operate in the alternate paper discharge operation mode (step s47). If the paper to be printed is coated paper (step s44, Yes), it is determined whether the color toner printing rate is 50% or more (step s45). If the color toner printing rate is not 50% or more (step s45, No), it is determined that it is not necessary to operate in the alternate paper discharge operation mode (step s47). On the other hand, when the color toner printing rate is 50% or more (step s45, Yes), it is determined that it is necessary to operate in the alternate paper discharge operation mode (step s46).

Next, the image page order / paper discharge mode determination process will be described with reference to FIG.
The printer control unit 100 determines whether the immediately preceding job has been operated in the alternate paper discharge operation mode (step s50). When not operating in the alternate discharge operation mode (step s50, No), the discharge mode of the first sheet is set to straight discharge, and the subsequent sheets are reversed as straight discharge for each sheet. It is set so as to be switched alternately by the paper discharge (step s54), and the order of the image pages on the front and back sides of the paper to be reversed is discharged (step s55).

  On the other hand, when the immediately preceding job is operated in the alternate sheet discharge operation mode (step s50, Yes), it is determined whether or not the sheet discharge tray is the same as the immediately preceding job (step s51). If the paper discharge tray is not the same as the previous job (No at step s51), the process at step s54 is executed. If the paper discharge tray is the same as the previous job (step s51, Yes), it is determined whether the paper discharge mode of the paper discharged at the end of the previous job is straight paper discharge (step s52). . If it is not straight paper discharge (step s52, No), the processing of step s54 is executed. In the case of straight discharge (step s52, Yes), the discharge mode of the first paper is set to reverse discharge, and the subsequent paper is switched alternately between straight discharge and reverse discharge for each paper. (Step s53).

  Next, the front side image and the back side image of the paper for which reverse paper discharge is set are switched to the reverse of the paper for which straight paper discharge is set (step s55).

  In the above, if the discharge mode of the paper discharged at the end of the previous job is straight discharge, the discharge mode of the top paper is set to reverse discharge and the paper is discharged at the end of the previous job When the paper discharge mode is reverse paper discharge, the first paper discharge mode is set to straight paper discharge. For this reason, it is possible to prevent the paper discharged at the end of the immediately preceding job from sticking to the paper discharged at the beginning of the next job.

  As described above, in the image forming apparatus of the present invention, when performing duplex printing, straight discharge and reverse discharge are alternately switched for each sheet to be discharged to prevent the sheets from being easily stuck. In this case, the sheet is discharged face up in straight sheet discharge, and faced down in reverse sheet discharge. Therefore, if printing is performed without replacing the front image and the back image, the image page order of the printed matter is reversed for each page. Therefore, by replacing the front side image and the back side image of the paper for which the reverse discharge is set with the straight discharge and the reverse discharge, a printed matter according to the page order can be obtained.

In the above-described embodiment, the alternate discharge operation mode in which straight discharge and reverse discharge are alternately performed has been described. However, discharge using a detour conveyance unit may be performed as non-reverse discharge.
Below, other embodiment which has a detour conveyance part is described.
In addition, about the structure similar to the said embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted or simplified.

As shown in FIG. 11, the image forming apparatus 1 a according to this embodiment includes an intermediate conveyance roller 34, a registration roller 38, a secondary transfer roller 16, a fixing unit 40, a conveyance roller 41, and a conveyance roller 51 from the sheet feeding cassettes 30 and 32. , 52 to the paper discharge roller 42 is provided. These rollers and the conveyance path 35 constitute a non-reverse conveyance unit. Further, a part of the conveyance path 35 from the conveyance roller 41 to the discharge roller 42 via the conveyance rollers 51 and 52 constitutes a detour conveyance path 50, and the conveyance rollers 51 and 52 and the detour conveyance path 50 are The detour conveyance unit of the present invention is configured. As in the above embodiment, a part of the reverse conveyance path 45 and the conveyance / reverse roller 44 constitute a second paper reversing unit, and a part of the reverse conveyance path 45 and the ADU reverse roller 46 are the first paper. Configure the reversing unit.
The path length of the detour conveyance unit is longer than the straight conveyance unit of the embodiment, that is, the path length for discharging the paper straight.

The path length of the detour conveyance unit between the conveyance roller 41 and the paper discharge roller 42 and the path length of the path via the second paper reversing unit are set to be substantially the same, and preferably the same path length. Set to.
Further, instead of setting the path length to be the same, the conveyance time passing through the detour conveyance unit and the conveyance time passing through the second sheet reversing unit may be set to be substantially the same. Also in this case, preferably, the same conveyance time is set.

  In the above, by making the path length or the required time substantially the same, the non-reverse paper discharge bypassing the second paper reversing unit and the reverse paper discharge via the second paper reversing unit are alternated. In this case, it is possible to perform alternate sheet discharge without requiring special adjustment of the gap between the sheets and the conveyance speed. In this case, continuous sheets on the downstream side of the detour conveyance unit and the second sheet reversing unit There is no interference.

FIG. 12 shows a control block of the image forming apparatus 1a.
The printer control unit 100 includes a fixing unit 40, an operation panel 80, a current reading unit 90, an image forming unit 110, a paper feeding unit 120, a registration transport unit 130, a bypass paper discharge unit 170, a reverse discharge unit, as in the above embodiment. A paper unit 150 and an ADU transport unit 160 are connected. These configurations are the same as in the above embodiment.

Further, the bypass control unit 170 is connected to the printer control unit 100 in a controllable manner.
The bypass paper discharge unit 170 controls the paper S that has passed through the fixing unit 40 to be discharged by the transport roller 41, the transport rollers 51 and 52, and the paper discharge roller 42 through the bypass transport path 50 without reversing the front and back sides. Is a unit.

  The basic operation of the image forming apparatus 1a will be described below. The toner image transferred to the paper S is sent through the conveyance path 35 and is fixed to the paper S by heat melting in the fixing unit 40. Thereafter, the sheet S is discharged from the discharge roller 42 to the discharge tray 70 through the detour conveyance unit or the second sheet reversing unit. In this embodiment, the paper discharge is performed by one of two types of paper discharge modes: a non-reverse paper discharge that bypasses the second paper reversing unit by the detour conveyance unit, and a reverse paper discharge through the second paper reversing unit. Done.

FIG. 13 shows a paper transport operation for paper discharge bypassing the second paper reversing unit.
In the paper discharge that bypasses the second paper reversing unit, the paper S that has passed through the fixing unit 40 and the transport roller 41 is switched by a switching gate (not shown) under the control of the bypass paper discharge unit 170, so that the paper is bypassed. The paper is conveyed through the path 50 via the conveying rollers 51 and 52, and is discharged to the paper discharge tray 70 through the paper discharge roller 42. At this time, the paper is discharged without being reversed.

  Next, FIG. 14 shows a paper transporting operation of the reverse paper discharge through the second paper reversing unit. In the reverse paper discharge, the reverse direction of the paper S that has passed through the fixing unit 40 and the transport roller 41 is switched by a switching gate (not shown) under the control of the reverse paper discharge unit 150, so that the reverse transport path 45 and the transport / reverse roller 44. It is conveyed to the side. At this time, the transport / reverse roller 44 is driven to rotate forward, and transports the paper S downward through the reverse transport path 45. Thereafter, the transport / reverse roller 44 is driven in reverse to transport the paper S through the reverse transport path 45 to the discharge roller 42 side. As a result, the sheet S is turned upside down. The sheet S with the front and back sides reversed is discharged to the discharge tray 70 through the discharge roller 42.

  Between the conveyance by the detour conveyance unit and the paper between the second paper reversing unit, the upstream paper interval before that is substantially maintained by setting the path length and the conveyance time of both.

Note that the image forming apparatus 1a of the present invention has a double-sided printing mode in which image printing is possible on both the front and back sides of the paper, as with the image forming apparatus 1. FIG. 15 shows the operation in the duplex printing mode.
The sheets S stacked and housed in the sheet feeding cassettes 30 and 32 are straightly conveyed to the secondary transfer roller 16 through the conveyance path 35 via the intermediate conveyance roller 34 and the registration roller 38 under the control of the registration conveyance unit 130. . Then, the toner image is transferred to one side of the sheet S by the secondary transfer roller 16 and fixed to the sheet S by the fixing unit 40.

  The sheet S that has passed through the fixing unit 40 and the transport roller 41 is transported to the transport / reverse roller 44 side through the reverse transport path 45 by switching a switching gate (not shown), and the reverse transport path is driven by the transport / reverse roller 44 that is normally driven. It is conveyed to the downstream side of 45 and conveyed to the ADU reversing roller 46 that is normally driven. The paper S transported to the ADU reverse roller 46 is temporarily stopped at that position, and thereafter, the ADU reverse roller 46 is driven in reverse to be transported to the ADU intermediate transport roller 48 side. Be transported. At this time, the sheet S is conveyed reversely to the registration roller 38 with the front and back sides reversed.

Then, the sheet S conveyed to the registration roller 38 is conveyed to the secondary transfer roller 16 through the conveyance path 35, the toner image is transferred to the other surface of the sheet S, and the fixing unit 40 fixes the toner image. Is called. Thereafter, the sheet S is discharged to the discharge tray 70 through the discharge roller 42.
Also in this embodiment, when performing printing in the duplex printing mode, there is an alternate paper discharge operation mode that prevents the sheets from adhering to each other by alternately performing the above-described non-reverse detour paper discharge and reverse paper discharge. ing.

Hereinafter, a printing procedure in the image forming apparatus 1a will be described with reference to a flowchart of FIG. The following procedure is executed by the printer control unit 100.
When the user performs an operation to start printing from the operation panel 80, it is determined whether or not the received job needs to be operated in the alternate paper discharge operation mode for preventing sticking between sheets (step s60). The alternate paper discharge operation mode is an operation mode in which discharge is performed by alternately switching between paper discharge bypassing the paper reversing unit and reverse paper discharge for each paper to be discharged. Note that the necessity determination process for the alternate paper discharge operation mode is performed in the same manner as in the image forming apparatus 1, whether or not the high gloss mode is selected, whether or not the clear toner printing rate is a predetermined value (for example, 30%) or more, Whether or not is greater than or equal to a predetermined value. Specifically, for example, it can be executed according to the flowcharts shown in FIGS. This processing procedure is also executed under the control of the printer control unit 100. However, in the present invention, the method for determining whether or not the alternate paper discharge operation mode is necessary is not limited to the above, and the necessity for the alternate paper discharge operation mode may not be determined.

  Next, it is determined whether or not the alternate paper discharge operation mode is necessary. If the alternate paper discharge is necessary (Yes in step s61), the non-reversed paper discharge by the detour conveyance unit is performed for each paper included in the job. The alternate paper discharge mode for switching between the reverse paper discharge by the second paper reversing unit is set, the image page order is reversed for each paper, and the image page order and the paper discharge mode are determined (step) s62). If it is determined in step s61 that replacement paper discharge is not required (step s61, No), the paper discharge mode is set to the user designation mode, and the image page order is set to the default setting (step s63). The default setting is usually forward or reverse.

The image page order / discharge mode determination process will be described with reference to FIG.
The printer control unit 100 determines whether the immediately preceding job has been operated in the alternate paper discharge operation mode (step s80). When not operating in the alternate paper discharge operation mode (No at step s80), the paper discharge mode of the first paper is set to non-inverted bypass paper discharge using a bypass transport unit, and the subsequent paper is in the paper discharge mode. Is set so as to be alternately switched between the bypass discharge and the reverse discharge for each sheet (step s84), and the image page order of the front and back sides of the sheet to be reversed is changed (step s85).

  On the other hand, if the immediately preceding job has been operated in the alternate discharge operation mode (step s80, Yes), it is determined whether or not the discharge tray is the same as the immediately preceding job (step s81). If the paper discharge tray is not the same as the previous job (step s81, No), the process of step s84 is executed. If the paper discharge tray is the same as the previous job (step s81, Yes), it is determined whether or not the paper discharge mode of the paper discharged at the end of the previous job is bypass discharge (step s82). . If it is not detour paper discharge (No at step s82), the process of step s84 is executed. In the case of bypass discharge (step s82, Yes), the discharge mode of the first sheet is set to reverse discharge, and the subsequent sheets are alternately switched between bypass discharge and reverse discharge for each sheet. (Step s83).

  Next, the front side image and the back side image of the sheet for which reverse discharge is set are switched to the reverse of the sheet for which bypass discharge is set (step s85).

Paper printing processing is performed according to the paper discharge mode determined in step s62 and the image page order (step s64).
In the paper printing process (step s64), an instruction is issued to the image forming unit 110, the fixing unit 40, and the like to execute the printing process (image formation, fixing, etc.) for one sheet. At this time, the image formation on the paper is performed in the order of the image pages determined in the process of step s62 or step s63.

Next, it is confirmed whether there is no paper or jam has occurred (step s65). If there is no sheet and no jam has occurred (step s65, No), the process waits until the printing process for one sheet is completed (step s66, No).
If there is no paper or jam occurs during the printing process on the paper (step s65, Yes), the printing process on the paper is interrupted (step s71), and the process waits until the recovery process is completed (step s72, No). ). In the recovery process, replenishment of paper, removal of Jam paper, and the like are performed. When the recovery process is completed (step s72, Yes), the printing process is resumed from the interrupted sheet (to step s64).

When the printing process is completed (step s66, Yes), it is determined whether or not the paper discharge mode of the paper for which the printing process has been completed is reverse discharge (step s67). In the alternate paper discharge operation mode, a paper discharge mode different from the previous paper discharge mode is set. That is, when the previous discharge is reverse paper discharge, it is not reverse paper discharge (step s67, No), and the bypass paper discharge unit 170 is instructed to execute the bypass paper discharge (step s68). Is the reverse paper discharge (step s67, Yes), and instructs the reverse paper discharge unit 150 to execute the reverse paper discharge (step s69).
In the case of non-alternating paper discharge mode, in the case of non-reverse paper discharge (step s67, No), an instruction is given to the bypass paper discharge unit 170 to perform bypass paper discharge (step s68). In reverse paper discharge (step s67, Yes), the reverse paper discharge unit 150 is instructed to execute reverse paper discharge (step s69).

  After executing the paper discharge process (step s68 or step s69), the printer control unit 100 checks whether or not the paper on which the paper discharge process has been executed is the final paper of the job being executed (step s70). If it is not the final sheet (step s70, No), a sheet printing process on the next sheet (step s64) is executed. If it is the last sheet (step s70, Yes), the process is terminated.

  As described above, when it is determined that it is necessary to operate in the alternate paper discharge operation mode, the non-reverse discharge and the reverse discharge that bypass the second paper reversing unit are alternately switched for each paper to be discharged. Since the paper is discharged, the positively charged surface and the negatively charged surface of the paper do not overlap each other, and sticking between the papers can be prevented.

  Also, in the above process, when there is no paper or jam occurs and printing is interrupted, the printing process is resumed from the interrupted paper. When resuming, the paper is ejected according to the paper ejection mode set for each paper, so the paper ejection mode for the paper ejected immediately before the interruption is different from the paper ejection mode for the paper to be resumed (interruption). Reverse discharge when the paper discharged immediately before is bypass discharge, and bypass discharge when the paper discharged immediately before interruption is reverse discharge. For this reason, even if printing is interrupted, it is possible to prevent the paper ejected immediately before the interruption and the paper ejected immediately after restarting from being easily stuck.

  Further, in the image forming apparatus of the above embodiment, when the path length or the required time is approximately the same, when the paper discharge bypassing the second paper reversing unit and the paper reversing unit paper discharge are alternately performed, The timing of the paper discharge operation by the paper roller 42 is set to an appropriate interval, and the order of paper discharge can be maintained properly.

  In each of the embodiments described above, the image forming apparatus includes the second sheet reversing unit and the image forming apparatus executes the alternate paper discharge operation mode. However, the second sheet reversing unit is provided outside the image forming apparatus. In the image forming system provided in the apparatus and including the image forming apparatus and the external apparatus, the alternate paper discharge operation mode may be executed.

Next, an embodiment of an image forming system including the external device will be described with reference to FIG. In addition, about the structure similar to the said embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted or simplified.
The image forming system includes an image forming apparatus 1b and a relay device 20 that is an external device. Although not shown, a post-processing device that performs predetermined post-processing on the downstream side of the relay device 20 may be provided. In the post-processing apparatus, appropriate post-processing such as punching, stapling, and folding is performed. In this embodiment, the second paper reversing unit is described as being provided in the relay device 20, but the post-processing device may be provided with a second paper reversing unit. In this case, the post-processing device corresponds to an external device.

Similar to the image forming apparatuses 1 and 1a, the image forming apparatus 1b includes a printer 10, an operation panel 80, and a document reading unit 90.
A transfer belt 12 is disposed at the center of the printer 10. On the side surface of the transfer belt 12, five image forming units 14CL, 14Y, 14M, 14CY, and 14K (in order of clear, yellow (Y), magenta (M), cyan (C), and black (K) from the top. In the following, the reference numerals are simplified and indicated by 14). Each image forming unit 14 has a photosensitive drum (not shown). Around each photosensitive drum, a charger for uniformly charging the surface of the photosensitive drum, an exposure unit for forming an electrostatic latent image according to image data on the surface of the uniformly charged photosensitive drum, and the electrostatic latent image as a toner A developing device for developing the image is arranged (none of them are shown).

In addition, primary transfer rollers 15CL, 15Y, 15M, 15CY, and 15K (hereinafter, the reference numerals are simply indicated by 15) are disposed at positions facing the respective photosensitive drums with the transfer belt 12 interposed therebetween.
A secondary transfer roller 16 is disposed below the transfer belt 12. When performing secondary transfer, a negatively charged toner image is electrostatically attracted to the paper S by applying a high positive transfer voltage to the secondary transfer roller 16.

A fixing unit 40 for fixing the transferred toner image on the paper S is disposed on the downstream side of the secondary transfer roller 16.
Two-stage paper feed cassettes 30 and 32 are detachably disposed below the printer 10.
A conveyance path 35 is provided from the sheet feeding cassettes 30 and 32 to the sheet discharge roller 42 via the intermediate conveyance roller 34, the registration roller 38, the secondary transfer roller 16, and the fixing unit 40.

Further, on the downstream side of the fixing unit 40, the conveyance path 35 is a straight conveyance unit that extends straight. A reverse conveyance path 45 that branches from the conveyance path 35 via the switching gate 43 is positioned on the downstream side of the fixing unit 40, and the downstream side of the reverse conveyance path 45 is upstream of the registration rollers 38 and the conveyance path 35. Have joined.
A reversing conveyance path 45 near the switching gate 43 is provided with a conveyance / reversing roller 44. After reversing the front and back of the sheet conveyed to the reversing conveyance path 45, the reversing conveyance path 45 is turned to the discharge roller 42 side with the front and back reversed. Paper can be conveyed. The transport / reverse roller 44 and the reverse transport path in the vicinity thereof constitute a third paper reverse section.

The third paper reversing unit has a function of reversing the front and back of the paper and ejecting the paper out of the image forming apparatus 1b when ejecting the image-formed paper face down. By conveying the sheet through the straight conveyance unit, the sheet on which the image is formed can be discharged out of the image forming apparatus 1b face up.
Further, an ADU reverse roller 46 and an ADU intermediate transport roller 48 are provided on the downstream side of the reverse transport path 45. These rollers and the reverse conveyance path 45 constitute a reverse conveyance section, and a part of the reverse conveyance path 45 located near the upstream and downstream in the conveyance direction of the ADU reverse roller 46 and the ADU reverse roller 46 constitutes a first sheet reverse section. To do.

The conveyance path 35 extends inside the relay device 20 and further extends outside the relay device 20. The conveyance path 35 may be connected to the paper discharge unit outside the relay device 20 or may be connected to the post-processing device.
In the relay device 20, the conveyance path 35 is branched into a detour conveyance path 50 and a reverse conveyance path 60 via a conveyance roller 53. The detour conveyance path 50 and the reverse conveyance path 60 are merged by a discharge roller 54 on the downstream side. The detour conveyance path 50 is provided with conveyance rollers 51 and 52, and the reverse conveyance path 60 is provided with a conveyance / reverse roller 61.

  The detour conveyance path 50 and the conveyance rollers 51 and 52 constitute a detour conveyance section, and the reverse conveyance path 60 and the conveyance / reverse roller 61 constitute a second sheet reversal section. Between the conveyance roller 53 and the paper discharge roller 54, the path of the detour conveyance unit and the path via the second sheet reversing unit are set so that the path length is substantially the same or the conveyance time is substantially the same. Yes.

Next, control blocks of the image forming system will be described with reference to FIG.
The image forming apparatus 1b includes a printer control unit 100. The printer control unit 100 controls the entire image forming apparatus such as image formation on the paper S, conveyance and discharge of the paper S, and a CPU, a program for operating the CPU, and a storage unit such as a ROM and a RAM. It is constituted by. The printer control unit 100 corresponds to the control unit of this embodiment.

  The printer control unit 100 is further connected to a document reading unit 90, an operation panel 80, an image forming unit 110, a fixing unit 40, a paper feeding unit 120, a resist conveyance unit 130, and an ADU conveyance unit 160 in a controllable manner. The functions of these units are the same as in the above embodiment.

  The relay device 20 includes a relay device control unit 200. The relay device control unit 200 controls the entire relay device 20 in response to an instruction from the printer control unit 100, and includes a CPU, a program for operating the CPU, and a storage unit such as a ROM and a RAM. .

  Further, a bypass paper discharge unit 210 is connected to the relay device control unit 200 in a controllable manner. The bypass paper discharge unit 210 causes the paper S transported into the relay device 20 through the transport path 35 to be downstream in the paper discharge direction by the bypass transport path 50 without reversing the front and back by switching operation of a switching gate (not shown). This is a control unit for discharging paper.

Further, a reverse discharge unit 220 is connected to the relay device control unit 200 in a controllable manner. The reverse paper discharge unit 220 transports the paper S transported into the relay device 20 through the transport path 35 to the reverse transport path 60 by a switching operation of a switching gate (not shown), and reverses the front and back of the paper by the transport / reverse roller 61. This is a control unit that performs discharge and discharges paper downstream in the paper discharge direction.
The bypass discharge path 50 and the reverse discharge path 60 are controlled by the printer control unit 100 via the relay device control unit 200.

The operation of the image forming system of this embodiment will be described below.
The paper S for which image forming processing has been completed by the printer 10 is non-reversed or reversed according to the face-up or face-down setting, and is conveyed to the relay device 20 through the conveyance path 35 by the paper discharge roller 42. The non-reverse paper discharge or the reverse paper discharge is executed in the same mode for each job or in the range of a section such as a chapter. In non-reverse paper discharge, the paper is discharged by straight conveyance, and in reverse paper discharge, the third paper reversing unit reverses the front and back of the paper and discharges it.

The relay device 20 can perform discharge in two types of modes, that is, non-inverted detour discharge and reverse discharge in which the second sheet reversing unit reverses the front and back of the sheet.
In the bypass discharge mode, the sheet S conveyed from the image forming apparatus 1b is discharged to the downstream side in the sheet discharge direction through the bypass conveyance path 50 without being reversed. In this mode, the conveyed paper S is discharged to the downstream side in the paper discharge direction with the front and back sides reversed via the reverse conveyance path 60.

Next, FIG. 20 shows a paper discharge operation through the detour conveyance path 50 in the relay device 20.
The sheet S conveyed from the image forming apparatus 1b to the relay apparatus 20 is introduced into the detour conveyance path 50 by a switching gate (not shown) via the conveyance roller 53, and conveyed to the paper discharge roller 54 via the conveyance rollers 51 and 52. The paper is ejected. These operations are controlled by the printer control unit 100.

Next, a paper discharge operation through the reverse conveyance path 60 in the relay device 20 is shown in FIG.
The sheet S transported from the image forming apparatus 1b to the relay apparatus 20 is transported by the forward rotation driving of the transport / reverse roller 60 while being introduced into the reverse transport path 60 by the switching gate (not shown) via the transport roller 53, and then transported. When the reverse roller 60 is driven in reverse to reach the paper discharge roller 54 from the reverse conveyance path 60, the front and back sides are reversed and the paper is discharged. These operations are controlled by the printer control unit 100.

In the present embodiment, the relay device 20 has an alternate discharge operation mode in which the bypass discharge and the reverse discharge are alternately performed.
Hereinafter, a procedure for printing in the image forming apparatus 1b and discharging in the relay apparatus 20 will be described based on a flowchart of FIG. The following procedure is executed by the printer control unit 100.

When the user performs a print start operation from the operation panel 80, it is determined whether or not the received job is required to be operated in the alternate paper discharge operation mode for preventing the sheets from sticking to each other (step s90). The alternate paper discharge operation mode is an operation mode in which discharge is performed by alternately switching between paper discharge bypassing the paper reversing unit and reverse paper discharge for each paper to be discharged.
Note that the necessity determination process for the alternate paper discharge operation mode is performed in the same manner as in the image forming apparatus 1, whether or not the high gloss mode is selected, whether or not the clear toner printing rate is a predetermined value (for example, 30%) or more, Whether or not is greater than or equal to a predetermined value. Specifically, for example, it can be executed according to the flowcharts shown in FIGS. This processing procedure is also executed under the control of the printer control unit 100. However, in the present invention, the method for determining whether or not the alternate paper discharge operation mode is necessary is not limited to the above, and the necessity for the alternate paper discharge operation mode may not be determined.

  It is determined whether the alternate discharge operation mode is necessary. If alternate discharge is necessary (Yes in step s91), the bypass discharge and the reverse discharge are switched for each sheet included in the job. The alternate paper discharge mode is set, the image page order is reversed for each sheet, and the image page order and paper discharge mode are determined (step s92).

If it is determined in step s91 that alternate paper discharge is not required (step s91, No), the paper discharge mode is set to the user designation mode, and the image page order is set to the default setting (step s93). The default setting is usually forward or reverse. The image page order / discharge mode determination process can be performed by the same procedure as the flowchart shown in FIG.
Paper printing is performed in accordance with the determined paper discharge mode and image page order (step s94).
In the paper printing process (step s94), the image forming unit 110, the fixing unit 40, and the like are instructed to execute the printing process (image formation, fixing, etc.) for one sheet. At this time, the image formation on the paper is performed in the order of the image pages determined in the process of step s92 or step s93.

Next, it is confirmed whether there is no paper or jam has occurred (step s95). If there is no sheet and no jam has occurred (step s95, No), the process waits until the printing process for one sheet is completed (step s96, No).
If no paper or jam occurs during the printing process on paper (Yes in step s95), the printing process on paper is interrupted (step s104), and the process waits until the recovery process is completed (No in step s105). ). In the recovery process, replenishment of paper, removal of Jam paper, and the like are performed. When the recovery process is completed (step s105, Yes), the printing process is resumed from the interrupted sheet (to step s94).

When the printing process is completed (step s96, Yes), it is determined whether the paper discharge in the image forming apparatus 1b is set to face up or face down (step s97). Face-up and face-down settings are made in advance and can be determined by initial settings or user settings.
When paper is discharged face up (step s97, face up), the paper is discharged from the image forming apparatus 1b through the straight conveyance unit without being turned over. When paper is discharged face down (step s97, face down), the paper is reversed from the front and back by the third paper reversing unit and discharged from the image forming apparatus 1b.

Next, it is determined whether or not the sheet discharge mode of the sheet discharged from the image forming apparatus 1b and conveyed to the relay apparatus 20 is reverse sheet discharge (step s100). In the alternate paper discharge operation mode, a paper discharge mode different from the previous paper discharge mode is set. That is, if the previous discharge is reverse paper discharge, it is not reverse paper discharge (No in step s100), and bypass paper discharge is executed (step s101). If the previous discharge is a bypass discharge, the reverse discharge is assumed (step s100, Yes), and the reverse discharge is executed (step s102).
If it is determined that the paper discharge mode is not the alternate paper discharge mode (No in step s100), the bypass paper discharge is executed (step s101). If it is determined that the paper is reversed (step s100, Yes), the paper is reversed (step s102).

  After executing the paper discharge process (step s101 or step s102), the printer control unit 100 checks whether or not the paper on which the paper discharge process has been executed is the final paper of the job being executed (step s103). If it is not the final sheet (step s103, No), a sheet printing process on the next sheet (step s94) is executed. If it is the last sheet (step s103, Yes), the process is terminated.

  As described above, when it is determined that it is necessary to operate in the alternate discharge operation mode, the relay device 20 alternately switches between the bypass discharge and the reverse discharge for each sheet to be discharged. In addition, the positively charged surface and the negatively charged surface of the paper do not overlap each other, and the paper can be prevented from sticking in the paper discharge unit, the paper stack unit, or the like.

  Also, in the above process, when there is no paper or jam occurs and printing is interrupted, the printing process is resumed from the interrupted paper. When resuming, the paper is ejected according to the paper ejection mode set for each paper, so the paper ejection mode for the paper ejected immediately before the interruption is different from the paper ejection mode for the paper to be resumed (interruption). Reverse discharge when the paper discharged just before bypasses the paper reversing portion, reverse discharge when the paper discharged immediately before interruption is reverse discharge, paper discharge bypassing the paper reversing portion). For this reason, even if printing is interrupted, it is possible to prevent the paper ejected immediately before the interruption and the paper ejected immediately after restarting from being easily stuck.

In the above embodiment, the second paper reversing unit is provided outside the image forming apparatus including the first paper reversing unit and the third paper reversing unit. However, the first paper reversing unit is provided in the image forming apparatus. The second paper reversing unit may be provided together with the first paper reversing unit and the third paper reversing unit.
FIG. 23 shows an image forming apparatus 1c having first to third sheet reversing units. In addition, the same code | symbol is attached | subjected about the structure similar to each above-mentioned embodiment, and the description is abbreviate | omitted or simplified.

  Similar to the image forming apparatuses 1, 1 a, and 1 b, the image forming apparatus 1 c includes a printer 10, an operation panel 80, and a document reading unit 90. A transfer belt 12 is disposed at the center of the printer 10. On the side surface of the transfer belt 12, five image forming units 14CL, 14Y, 14M, 14CY, and 14K (in order of clear, yellow (Y), magenta (M), cyan (C), and black (K) from the top. In the following, the reference numerals are simplified and indicated by 14). Each image forming unit 14 has a photosensitive drum (not shown). Around each photosensitive drum, a charger for uniformly charging the surface of the photosensitive drum, an exposure unit for forming an electrostatic latent image according to image data on the surface of the uniformly charged photosensitive drum, and the electrostatic latent image as a toner A developing device for developing the image is arranged (none of them are shown).

  In addition, primary transfer rollers 15CL, 15Y, 15M, 15CY, and 15K (hereinafter, the reference numerals are simply indicated by 15) are disposed at positions facing the respective photosensitive drums with the transfer belt 12 interposed therebetween. A secondary transfer roller 16 is disposed below the transfer belt 12. When performing secondary transfer, a negatively charged toner image is electrostatically attracted to the paper S by applying a high positive transfer voltage to the secondary transfer roller 16.

A fixing unit 40 for fixing the transferred toner image on the paper S is disposed on the downstream side of the secondary transfer roller 16. Two-stage paper feed cassettes 30 and 32 are detachably disposed below the printer 10.
A conveyance path 35 is provided from the sheet feeding cassettes 30 and 32 to the sheet discharge roller 54 via the intermediate conveyance roller 34, the registration roller 38, the secondary transfer roller 16, and the fixing unit 40.
On the downstream side of the fixing unit 40, a straight conveyance unit that extends straight is provided. A reverse conveyance path 45 that branches from the conveyance path 35 via the switching gate 43 is positioned on the downstream side of the fixing unit 40, and the downstream side of the reverse conveyance path 45 is upstream of the registration rollers 38 and the conveyance path 35. Have joined.

  A reversing / conveying roller 44 is provided in the reversing conveyance path 45 near the switching gate 43. After reversing the front and back of the sheet conveyed to the reversing conveying path 45, the sheet is conveyed to the conveying roller 53 side with the front and back reversed. Can be transported. The transport / reverse roller 44 and the reverse transport path in the vicinity thereof constitute a third paper reverse section. The third paper reversing unit has a function of reversing the front and back of the paper and ejecting the paper out of the image forming apparatus 1c when ejecting the paper on which the image has been formed face down. By conveying the sheet through the straight conveyance unit, the sheet on which the image is formed can be discharged out of the image forming apparatus 1c face up.

  Further, an ADU reverse roller 46 and an ADU intermediate transport roller 48 are provided on the downstream side of the reverse transport path 45. These rollers and the reverse conveyance path 45 constitute a reverse conveyance section, and a part of the reverse conveyance path 45 located near the upstream and downstream in the conveyance direction of the ADU reverse roller 46 and the ADU reverse roller 46 constitutes a first sheet reverse section. To do.

  The conveyance path 35 further extends downstream in the paper discharge direction, and branches into a bypass conveyance path 50 and a reverse conveyance path 60 via a conveyance roller 53. A switching gate (not shown) is provided at the branch portion. The detour conveyance path 50 and the reverse conveyance path 60 are merged in the vicinity of the discharge roller 54 on the downstream side. The detour conveyance path 50 is provided with conveyance rollers 51 and 52, and the reverse conveyance path 60 is provided with a conveyance / reverse roller 61.

  The detour conveyance path 50 and the conveyance rollers 51 and 52 constitute a detour conveyance unit that detours the reverse conveyance path 60, and the reverse conveyance path 60 and the conveyance / reversal roller 61 constitute a second sheet reversal unit. The detour conveyance unit and the second sheet reversing unit are set so that the path length is substantially the same or the conveyance time is substantially the same.

  The sheet that has reached the conveyance roller 53 can be selected by performing detour conveyance and reverse conveyance within the image forming apparatus 1c, and can be discharged in an alternate discharge operation mode.

  In each of the above-described embodiments, the operation in the alternate paper discharge operation mode when the duplex printing mode is set is described. However, when the simplex printing mode is set, the surface on which image printing is performed is described. It is also possible to set a blank image as an image to be printed on the opposite side, perform double-sided printing, and operate in the alternate paper discharge operation mode.

  In each of the embodiments described above, the bypass conveyance unit is described as being provided with a bypass conveyance unit and a bypass conveyance unit and a second sheet reversing unit. A conveyance unit, a straight conveyance unit, and a sheet reversing unit may be provided.

FIG. 24 shows a main part of an example in which the conveyance path is branched.
The conveyance path 35 branches to a detour conveyance path 50, a reverse conveyance path 60, and a straight conveyance path 70 via a conveyance roller 53, and the conveyance paths are joined by a discharge roller 54. The detour conveyance path 50 and the straight conveyance path 70 convey the paper in a non-inverted manner, and the reverse conveyance path 60 reverses the front and back of the paper and discharges the paper. When performing non-reversed paper discharge, detour conveyance and straight conveyance can be selected. If the distance between the sheets is sufficient and there is no interference with the reversely transported paper, straight transport can be selected, and if there is interference with the reversely transported paper, detour transport can be selected. .

  As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to the content of the said embodiment, Of course, unless it deviates from this invention, an appropriate change is possible.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1a Image forming apparatus 1b Image forming apparatus 1c Image forming apparatus 10 Printer 12 Transfer belt 14 Image forming unit 16 Secondary transfer roller 20 Relay device 34 Intermediate conveyance roller 38 Registration roller 40 Fixing unit 42 Paper discharge roller 44 Reverse roller 46 ADU reverse roller 48 ADU intermediate transport roller 50 Detour transport path 60 Reverse transport path 70 Paper discharge tray 80 Operation panel 90 Document reading unit 100 Printer control unit 110 Image forming unit 120 Paper feed unit 130 Resist transport unit 140 Straight paper discharge Part 150 Reverse paper discharge part 160 ADU transport part S Paper

Claims (22)

An image forming unit that prints an image on paper based on image data;
The non-reversing conveyance unit that conveys the sheet to the downstream side in the paper discharge direction without reversing the front and back through the image forming unit and the sheet conveying direction of the image forming unit by reversing the front and back of the sheet printed on one side A transport unit having a reverse transport unit for transporting upstream;
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the front and back of the sheet conveyed by the reversing conveyance unit;
A second paper reversing unit that is provided in the transport unit from the image forming unit to the downstream side in the paper discharge direction and reverses the front and back of the paper transported by the transport unit;
A control unit that controls the image forming unit and the transport unit;
The control unit includes the one-sided printing mode in which an image can be printed on the front side of the sheet by conveyance in the non-reversing conveyance unit, conveyance in the non-reversing conveyance unit, and reversal conveyance in the reverse conveyance unit. A double-sided printing mode in which images can be printed on the front and back of the paper, and at least in the double-sided printing mode, after the image is printed on the front and back of the paper by the image forming unit, the front and back of the paper are reversed by the second paper reversing unit. A non-reverse paper discharge operation for discharging paper without being reversed and a reverse paper discharge operation for performing paper discharge by reversing the front and back of the paper at the second paper reversing unit are alternately performed for each paper to be discharged. An image forming apparatus having a paper discharge operation mode.   The image forming apparatus according to claim 1, wherein the non-reversing conveyance unit includes a straight conveyance unit that discharges the paper straight.   The non-reversing conveyance unit includes a detour conveyance unit, and the detour conveyance unit has a longer path length than a path for discharging the paper straight without passing through the detour conveyance unit. The image forming apparatus according to 1 or 2.   The path length of the detour conveyance unit and the path length via the second sheet reversing unit are merged between the path of the detour conveyance unit and the path via the sheet reversing unit between continuously conveyed sheets. The image forming apparatus according to claim 2, wherein the image forming apparatus has a relationship not to interfere with each other on the downstream conveyance unit.   5. The image forming apparatus according to claim 2, wherein a path length of the detour conveyance unit and a path length through the second sheet reversing unit are substantially the same.   The conveyance time during which the sheet is conveyed through the detour conveyance unit and the conveyance time during which the sheet is conveyed through the second sheet reversing unit are determined as follows. The image forming apparatus according to claim 2, wherein the image forming apparatus has a relationship not to interfere with each other on the downstream conveyance unit where the path via the reversing unit merges.   7. The transport time for transporting the paper through the detour transport unit and the transport time for transporting the second paper through the second paper reversing unit are substantially the same. The image forming apparatus described in the item.   In the alternate paper discharge operation mode, the control unit prints the front image printed on the paper by performing image formation on the paper on which the non-reverse paper discharge operation is performed and image formation on the paper on which the reverse paper discharge operation is performed. The image forming apparatus according to claim 1, wherein the page order of the reverse image and the reverse image is printed with each sheet being reversed.   The image forming apparatus according to claim 1, wherein the control unit performs the alternate paper discharge operation mode only in a duplex printing mode.   10. The image formation according to claim 1, wherein the control unit operates in the alternate paper discharge operation mode when printing is performed using clear toner in the image forming unit. apparatus.   The image forming apparatus according to claim 1, wherein the control unit operates in the alternate paper discharge operation mode when a toner adhesion amount or a printing rate is equal to or greater than a predetermined value.   The image forming apparatus according to claim 1, wherein the control unit operates in the alternate paper discharge operation mode when a post-processing device is connected.   The image forming apparatus according to claim 1, wherein the control unit determines whether to operate in the alternate paper discharge operation mode based on the type of the paper.   When the single-sided printing mode is set, the control unit sets a blank image as an image to be printed on a paper surface opposite to the paper surface on which the image printing is performed, performs double-sided printing, and performs the alternate discharge. The image forming apparatus according to claim 1, wherein the image forming apparatus operates in an operation mode.   When starting the job in the alternate discharge operation mode, the control unit starts the job with the reverse discharge when the non-reverse discharge is performed at the end of the previous job, and the last of the previous job. The image forming apparatus according to claim 1, wherein when the reverse discharge is performed, the job is started by the non-reverse discharge.   When resuming printing interrupted during operation in the alternate paper discharge operation mode, the control unit performs the reverse paper discharge if the last normal paper discharge before the interruption is the non-reverse paper discharge. 16. The job is resumed at step S15, and when the reversely discharged operation is the last normal discharge before the interruption, the job is restarted with the non-reverse discharge. 2. The image forming apparatus according to item 1. An image forming unit that prints an image on paper based on image data;
The sheet printed on one side is reversed with a non-reversing conveying section that conveys the sheet to the downstream side in the paper discharge direction via the image forming section and a non-reversing conveying section that conveys the sheet via the image forming section. A transport unit having a reverse transport unit that transports the image forming unit to the upstream side in the paper transport direction;
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the sheet conveyed by the reversing conveyance unit;
A second paper reversing unit that is provided in the transport unit from the image forming unit to the downstream side in the paper discharge direction and reverses the paper transported by the transport unit;
A control unit that controls the image forming unit and the transport unit;
The control unit includes the one-sided printing mode in which an image can be printed on the front side of the sheet by conveyance in the non-reversing conveyance unit, conveyance in the non-reversing conveyance unit, and reversal conveyance in the reverse conveyance unit. A double-sided printing mode in which images can be printed on the front and back of the paper, and at least in the double-sided printing mode, after the image is printed on the front and back of the paper by the image forming unit, the front and back of the paper are reversed by the second paper reversing unit. A non-reverse discharge operation that discharges paper without being discharged and a reverse conveyance operation that reverses the front and back of the paper and discharges the paper at the second paper reversing section are alternately switched for each paper to be discharged. An image forming system having a paper operation mode.   18. The image forming system according to claim 17, wherein the non-reversing transport unit includes a straight transport unit that discharges the paper straightly downstream in the paper discharge direction.   The non-reversing conveyance unit includes a detour conveyance unit, and the detour conveyance unit has a longer path length than a path for discharging the paper straight without passing through the detour conveyance unit. Or the image forming system according to 18. An image forming unit that prints an image on paper based on image data;
A transport unit having a non-reverse transport unit that transports the paper through the image forming unit and a reverse transport unit that reverses the paper printed on one side and transports the paper upstream of the image forming unit in the paper transport direction; ,
A first sheet reversing unit that is provided in the reversing conveyance unit and reverses the sheet conveyed by the reversing conveyance unit;
A control unit according to any one of claims 1 to 19, and connected to a downstream side in a paper discharge direction of an image forming apparatus,
An external device comprising the second paper reversing unit according to claim 1. In an image forming method for printing an image on the front and back of a sheet based on image data,
An image is printed on the front and back of the paper by non-reversing transport that transports the paper without reversing and reversal transport that transports the paper by reversing the front and back of the paper, and then ejects the paper without reversing the front and back of the paper. A non-reverse paper discharge operation for discharging the paper downstream in the paper direction and a reverse paper discharge operation for reversing the front and back of the paper and discharging the paper downstream in the paper discharge direction are alternately switched for each paper to be discharged. An image forming method.   In the image formation on the paper subjected to the non-reverse conveyance and the image formation on the paper subjected to the reverse conveyance, the front side image and the back side image to be printed on the paper are printed in reverse order every other page. The image forming method according to claim 21, wherein:

Images